This invention relates to power supplies and more particularly relates to a novel control power supply for circuits containing high side switches.
Most power electronic equipment requires a control power supply that supplies power (5-20 w) for the control and drive circuits of the device. Typically, a flyback or a buck converter is used to provide the control power.
Referring to FIG. 1, a circuit diagram of a conventional flyback converter 2 is shown. In a typical application, flyback converter 2 is provided with a 300V input connected across a relatively large transformer 4. An extra clamp circuit 16 is required, such as would be provided by the arrangement of diode 6, resistor 8 and capacitor 10. A FET 12 is controlled by controller 14. The FET requires a breakdown voltage much greater than 300 V, typically from 450-660 V.
Another conventional solution, a buck power supply, is illustrated in the circuit diagram of FIG. 2. In the buck power supply of circuit 20, regulation takes place at the ground level. A level shifting driver 22 is used to drive the gate of the high side switch 24. In a 300 V application, FET 24 typically can have a voltage rating of 400 V.
The conventional circuits have various disadvantages. Flyback converters require transformers having a number of terminals, adding to size and cost. In addition, the converters have losses due to current flow through higher voltages, and thus require higher RDSON MOSFET switches. Conventional buck power supply topologies require a high voltage integrated circuit (HVIC).
The present invention overcomes the disadvantages of the prior art by providing a novel topology which uses a standard power supply controller to control a high side switch in an electronic circuit. In the power supply of the present invention, the feedback voltage referenced to a ground (or negative bus level) is level-shifted to a high side controller by means of a diode/capacitor/resistor network. In addition, power to a high side controller is supplied by using the feedback output voltage.